Yes so you always want to use RF first.
Quote from EJ http://elitistjerks.com/f74/t130590-...mastery_5_2_a/
Due to the Stampede pets working like normal, including focus use, you will ideally want to have them out while under focus regeneration effects like Rapid Fire and Focus Fire.
Stampede pets update stats dynamically, so whether you use Stampede before or after shortterm buffs are applied doesn't matter (in theory - how fast they update very likely depends on a few different factors, latency being chief amongst them)
Sec
-1 Prepot
0 Serpent Sting
1 Dire Beast
2 BW + AMoC + Rabid (Pet)
3 KC
4 Stampede
5 Arcane Shot
6 Arcane Shot
7 Arcane Shot
8 Arcane Shot
9 KC
10 Arcane Shot
11 Arcane Shot
12 Rapid Fire
13 Cobra Shot (When perfectly played, Serpent Sting wont fall off)
.
.
. (normal Rota: KC on cooldown, AS an Cobra Shot)
.
.
30 Serpent Sting (manual)
31 Dire Beast
32 Readiness
33 Dire Beast
34 BW + AMoC
35 KC
36 Arcane Shot
37 Arcane Shot
38 Arcane Shot
39 Arcane Shot
40 Arcane Shot
41 KC
42 Arcane Shot
43 Arcane Shot
44 Rapid Fire
45 Cobra Shot
.
.
.
(Never use BW with Rapid Fire, it just waste a mighty Dmg Cooldown)
See, now I'm reading BW + RF is a CD loss. I've always popped the CDs that don't benefit from BW (Dire Beast, Stampede, etc), then BW, KC/ArcS spam, THEN RF after BW is ended. Readiness and do that all again.
But now I'm seeing a lot of conflicting reports that makes me unsure.
Especially if you are using the newer beefier trinkets, generally with your initial Serpent you'll proc both trinkets and want to fit as much BW damage into that 20 seconds, if you pop your BW immediately after that initial serpent and use your cooldowns perfectly you'll fit 5 KC's into that 20 buff window, with a lovely KC crit (hopefully) in the last 2 seconds of Renataki's.